The present invention relates to a speed control system and method for automotive vehicles, and more particularly to an improvement of an electronic speed control system and method for an automotive vehicle of the type in which the fuel supply into the engine is controlled in accordance with a difference between the actual speed of the vehicle and a desired command speed in relation to the acceleration of the vehicle.
In such an electronic speed control system as disclosed in U.S. Pat. No. 4,250,854 issued on Feb. 17, 1981, in the name of Matsui et al., a speed-difference calculation circuit is provided to calculate an absolute value of a time difference between a predetermined period of time defined by the desired command speed and an instant period of time responsive to the actual vehicle speed, and an acceleration calculation circuit is further provided to calculate an absolute value of a time difference between the preceding and following instant periods of time responsive to the actual vehicle speed. Thus, a correction signal is produced in dependence upon the calculated absolute values to control the fuel supply into the engine so as to maintain the desired command speed of the vehicle.
In the above speed control system, a conventional speed sensor, for example, in the form of a magnetic pickup type transducer, is mounted, in general, on a portion of the vehicle body structure to detect the instant period of time responsive to the actual vehicle speed. This means that if there occurs an error in operation of the speed sensor due to mechanical vibration of the vehicle body structure, racing of the road wheels or the like, the respective absolute values will be erroneously calculated, resulting in an error of the correction signal for control of the fuel supply into the engine.